Anti-arrhythmic cardiac devices are well known in the art. Such devices include implantable and non-implantable devices which are used for detecting various types of arrhythmic conditions in a cardiac patient and for applying an appropriate anti-arrhythmic therapy to the heart.
For example, various pacemaker devices may detect various types of brady-arrhythmias (also known as bradycardias) and provide artificial pacing therapy to one or more cardiac chambers.
Other types of anti-arrhythmic devices such as cardiac defibrillators, and other anti-tachyarrhythmia devices such as defibrillator/cardioverter devices are designed to detect various different types of tachy-arrhythmias (also known as tachycardias) such as ventricular tachycardia (VT) which is a non-fibrillation type of tachy-arrhythmia and ventricular fibrillation (VF), and to provide one or more types of appropriate anti-tachycardia therapy to the heart such as anti-tachycardia pacing (ATP) therapy, cardioverting shock therapy and shock defibrillation therapy. Such devices may use multi-tiered tachy-arrhythmia detection algorithms (also known as classification algorithms) for distinguishing between VT, VF and supra-ventricular tachycardia (SVT) arising from atrial fibrillation and for applying the proper type of therapy selected from ATP therapy, low or medium energy cardioversion shock therapy, and high energy defibrillating shock therapy.
U.S. Pat. No. 4,403,614 to Engle et al titled “IMPLANTABLE CARDIOVERTER”, incorporated herein by reference, discloses an implantable cardioverter/defibrillator device capable of delivering cardioversion therapy pulses having an energy level lower than necessary for defibrillation as well as defibrillating pulses.
Some modern implantable Cardiotherapy devices are adapted to include a combination of various cardiac therapeutic modes. For example, implantable cardio-therapy devices may use a combination of anti-bradycardia pacing, ATP pacing, cardioversion and automatic defibrillating shock therapy. U.S. Pat. No. 4,830,006 to Haluska et al. titled “IMPLANTABLE CARDIAC STIMULATOR FOR DETECTION AND TREATMENT OF VENTRICULAR ARRHYTHMIAS”, incorporate herein by reference, discloses a cardiac stimulator device which integrates the functions of bradycardia and anti-tachycardia pacing therapies and cardioversion and defibrillation shock therapies.
Recently, a new method of cardiotherapy has been introduced for modifying the cardiac contractility by delivering non-excitatory electrical signals to the myocardium at a selected time such that the electrical signals do not result in exciting propagating myocardial action potentials due to myocardial refractoriness. While such non-excitatory electrical signals do not lead to propagating myocardial action potentials, they may modulate the myocardial contractility in naturally or artificially paced cardiac beats.
Devices for performing this contractility modulating cardiotherapy are known as excitable tissue control (ETC) devices, and are also known as cardiac contractility modulation (CCM) devices. It is noted that the terms CCM and ETC are interchangeably used throughout the present application and refer to methods for modulating cardiac contractility by delivering non-excitatory electrical signals to the heart. Similarly, the terms CCM device and ETC device are interchangeably used throughout the present application and refer to devices adapted for modulating cardiac contractility by delivering non-excitatory electrical signals to the heart.
ETC devices modulate the activity of excitable tissues by application of non-excitatory electrical signals to the heart (or other excitable tissues) through suitable electrodes in contact with the tissue. For example, ETC devices may be used, inter alia, to increase or decrease the contractility of cardiac muscle in vitro, in vivo and in situ., as disclosed in detail in PCT application, International Publication Number WO 97/25098 to Ben-Haim et al., titled “ELECTRICAL MUSCLE CONTROLLER”, incorporated herein by reference. Other methods and applications of ETC devices are disclosed in PCT applications commonly-assigned to the assignee of the present application, International Publication Number WO 98/10828, titled “APPARATUS AND METHOD FOR CONTROLLING THE CONTRACTILITY OF MUSCLES” to Ben Haim et al., incorporated herein by reference, International Publication Number WO 98/10829, titled “DRUG-DEVICE COMBINATION FOR CONTROLLING THE CONTRACTILITY OF MUSCLES” to Ben Haim et al., incorporated herein by reference and International Publication Number WO 98/10830, titled “FENCING OF CARDIAC MUSCLES” to Ben Haim et al., incorporated herein by reference, International Publications Number WO 98/10831 to Ben Haim et al., titled “CARDIAC OUTPUT CONTROLLER”, incorporated herein by reference.
Further applications of the ETC including devices combining cardiac pacing and cardiac contractility modulation are disclosed in PCT Application, International Publication No. WO 98/10832, titled “CARDIAC OUTPUT ENHANCED PACEMAKER” to Ben Haim et al., co-assigned to the assignee of the present application. Such ETC devices function by applying non-excitatory electrical field signals of suitable amplitude and waveform, appropriately timed with respect to the heart's intrinsic electrical activity to selected cardiac regions. The contraction of the selected regions may be modulated to increase or decrease the stroke volume of the heart. The timing of the ETC signals must be carefully controlled since application of the ETC signal to the myocardium at an inappropriate time may be arrhythmogenic. The ETC signals must therefore be applied to the selected cardiac region within a defined time interval during which the selected cardiac region will not be stimulated by the ETC signals.
As disclosed in International Publication No. WO 98/10832, the ETC signals may be timed relative to a trigger signal which is also used as a pacing trigger, or may be timed relative to locally sensed electrogram signals.
Co-pending U.S. patent application to Mika et al., Ser. No. 09/276,460, Titled “APPARATUS AND METHOD FOR TIMING THE DELIVERY OF NON-EXCITATORY ETC SIGNALS TO A HEART”, filed Mar. 25, 1999, assigned to the common assignee of the present application, the entire specification of which is incorporated herein by reference, and the corresponding PCT application, International Application No. PCT/IL00/00126, International Publication No. WO 00/57952, disclose a method for timing the delivery of non-excitatory ETC signals to a heart using, inter alia, an alert window period for reducing the probability of delivering an improperly timed ETC signal to the heart due to spurious detection of noise or ectopic beats.
Co-pending U.S. patent application Ser. No. 09/328,068 to Mika et al., titled “APPARATUS AND METHOD FOR COLLECTING DATA USEFUL FOR DETERMINING THE PARAMETERS OF AN ALERT WINDOW FOR TIMING DELIVERY OF ETC SIGNALS TO A HEART UNDER VARYING CARDIAC CONDITIONS”, filed Jun. 8, 1999, the entire specification of which is incorporated herein by reference, and the corresponding PCT application, International Application No. PCT/IL00/00310, disclose devices and methods for collecting patient data which is usable for the operation of a device for timing of delivery of ETC signals to the heart using, inter alia, a dynamically varying alert window period for event sensing.
Co-pending U.S. patent application Ser. No. 09/338,649 to Mika et al., titled “APPARATUS AND METHOD FOR SETTING THE PARAMETERS OF AN ALERT WINDOW USED FOR TIMING THE DELIVERY OF ETC SIGNALS TO A HEART UNDER VARYING CARDIAC CONDITIONS”, filed Jun. 23, 1999, the entire specification of which is incorporated herein by reference, and the corresponding PCT application, International Application No. PCT/IL00/00321, disclose devices and methods for timing of delivery of ETC signals to the heart using, inter alia, a dynamically varying alert window period for event sensing.
Application of ETC therapy to the heart may enhance the cardiac output without increasing the heart rate. Such therapy may be advantageously applied, inter alia, to patients having no diagnosed cardiac rhythm abnormalities as well as to patients such as congestive heart failure (CHF) patients which are particularly prone to episodes of VT or VF. Since cardiac patients such as, inter alia, CHF patients may benefit from the use of implantable or non-implantable anti-arrhythmic devices, such as defibrillator, Defibrillator/cardioverter devices and the like, it may be advantageous to implement a single device which is capable of delivering anti-arrhythmic therapy and ETC therapy to a cardiac patient. For example, such a device may be capable of delivering ETC therapy and defibrillating shock therapy to a patient, when a need for such therapy is detected.
While the various methods of timing the delivery of ETC signals to the heart disclosed in the above co-pending U.S. patent application Ser. Nos. 09/276,460, 09/328,068 and 09/338,649 to Mika et al., and in the corresponding PCT applications, greatly reduce the probability of inducing arrhythmias due to delivery of ETC signals to the heart at a vulnerable time, it may be desirable to include anti-arrhythmia capabilities in ETC or CCM devices as a safety device in case of occurrence of tachy-arrhythmia episodes such as VT or VF, either due to a delivered ETC signal or spontaneously.
Unfortunately, the delivery of ETC signals to the myocardium may lead to electrical artifact signals sensed by the sense electrodes of the anti-arrhythmic device. Such electrical artifact signals may be erroneously detected by the event detecting circuitry of the anti-arrhythmic device as electrical events representing cardiac activation. Such spurious detection of electrical artifacts induced by ETC signals may adversely affect the detection and/or classification of cardiac tachy-arrhythmias. For example, such spurious event detection may result in classification of a normal heart rate as VT or VF leading to unnecessary and potentially dangerous defibrillating shock therapy being delivered to the heart.
Besides the increased patient risk and patient discomfort caused by such unnecessary delivery of defibrillation shock therapy, such erroneous detection of VF followed by defibrillating shock therapy may lead to unnecessary drain on the battery of the device, thus shortening the useful life in implanted devices. Additionally, in devices capable of delivering cardioversion therapy, spurious event detection caused by ETC induced electrical artifacts may result in unnecessary delivery of cardioversion therapy by the device which has the disadvantage of unnecessary battery drain and which may increase patient risk.
Another problem which may result from delivering of ETC signals to the heart of a patient which is monitored by an anti-arrhythmic device such as, inter alia, a defibrillator/cardioverter device, is the possible interference of ETC induced electrical artifacts with the operation of detection circuitry utilizing automatic gain control (AGC) or automatic threshold control (ATC). AGC methods and ATC methods are well known in the art. For example, AGC and ATC methods are disclosed by Dennis A. Brumwell et al., in Chapter 14 titled “THE AMPLIFIER: SENSING THE DEPOLARIZATION” in the book titled “IMPLANTABLE CARDIOVERTER DEFIBRILLATOR THERAPY: THE ENGINEERING-CLINICAL INTERFACE”, pp. 275–302, Eds. Mark W. Kroll and Michael H. Lehmann, Kluwer Academic Publishers, USA, 1997.
ETC signal induced artifacts sensed by the defibrillator amplification circuits may cause an undesirable decrease in the gain of the amplifier circuits in defibrillators using AGC based algorithms which may lead to failure to detect VF signal. ETC signal induced artifacts sensed by the defibrillator amplification circuits may also cause an undesirable increase in the threshold level in defibrillators using ATC based algorithms which may also lead to failure to detect VF signal.
The above described interference problems may be encountered in the operation of a variety of different prior art internal cardiac defibrillator (ICD) devices and automatic internal cardioverter defibrillator (AICD) devices, including tiered therapy devices capable of delivering different types of cardiac therapy such as anti-brady-arrhythmic pacing therapy, anti-arrhythmic cardioversion therapy, anti-arrhythmic defibrillating shock therapy, variable energy shock therapy, anti-tachycardia pacing therapy (ATP) and any combination thereof. In the presence of ETC signals delivered by operating CCM or ETC devices.